Typically, aircraft fins whose inclination is changeable in relation to the longitudinal orientation of an aircraft fuselage are trimmed, i.e., their inclination in relation to the aircraft fuselage is changed, using trapezoidal thread spindles or recirculating ball spindles. Since very high requirements in regard to their reliability and/or breakdown probability must be placed on trim actuators of this type, two load paths must typically be provided, which may be implemented through a double spindle, for example. Alternatively to this, it is also possible to implement two load paths in only one spindle in the form of an integrated construction.
Implementations of trimmable horizontal stabilizer actuators in the form of recirculating ball spindles or trapezoidal thread spindles of this type are very complex because of the required redundancy and the required synchronization of the individual spindles. The number of components required is relatively large, because of which the implementation becomes relatively difficult. In addition, wear and in turn a corresponding play result due to the movable mechanical components of such spindles. In the extreme case, such play in the spindles may also result in undesired aeroelastic effects on the fins, which may finally even result in flapping of the wings.
In addition, the very complex constructions of these redundantly constructed trimmable horizontal stabilizer actuators may result in so-called sleeping faults if spindles are used, which are frequently not recognized in a timely manner. In order to nonetheless recognize faults of this type, a significant monitoring outlay is required, because of which the trim actuators become even more complex and heavy.
Since until now all conceivable efforts have been undertaken to optimize a trimmable horizontal stabilizer actuator using trapezoidal thread or recirculating ball spindles in regard to its breakdown probability in its weight, without this having resulted in significant improvements, there is still a need for a trimmable horizontal stabilizer actuator which has a light construction and reliably fulfills the enormous requirements on its breakdown probability.